Name__________________________________________ Period _____
INVESTIGATING THE VERTICAL THERMAL STRUCTURE OF THE OCEAN:
TEMPERATURE vs DEPTH AT THREE DIFFERENT LATITUDES.
INTRODUCTION
Water temperatures below the surface are measured using a bathythermograph, an electronic sensor that
keeps track of the various temperatures at prearranged depths from the surface to the bottom. Warm water
tends to be less dense and “floats” on the top of the ocean, where it is heated by the sun. Cold water is more
dense and sinks to the deep ocean floor. A third region in which the temperature changes most drastically
within a narrow range of depth is called the thermocline. In this investigation we will consider thestructure
of the 3-layer temperature profile from the surface (0 meters) down to 2,000 meters, and compare high
latitudes, middle latitudes and tropical waters. But remember, density causes the water layers to be arranged
the way they are.
PROCEDURES
Use a single sheet of your own graph paper to plot the following four sets of data on the same graph. Let
the x-axis represent temperature, from 0OC to 30OC, and let the y-axis represent depth, running from 0 m
at the top of your paper down to 2000 m near the bottom of your paper. Use a different color line to
represent each set of data. (low lat = low latitudes, tropical; mid lat = middle latitudes; high lat = high
latitudes, polar).
DATA
TEMPERATURE vs DEPTH
temperature (C)
tropical
polar
summer
mid latitudes
375
500
625
750
1000
1125
depth (meters)
875
(Example: y-axis runs
from 0 at top to 2000
at the bottom)
30
25
20
15
10
surface
5
250
1250
1375
1500
1625
high
lat
7.5
0
3.75
3.5
3.25
3
2.75
2.5
2.5
2.4
2.3
2.1
2
1.8
1.5
1.3
1.25
125
temperature (C)
mid lat
mid lat
summer winter
18
10.2
10.2
10.2
10.1
10.1
10
10
8.7
8.7
7.5
7.5
6.5
6.5
5.8
5.8
5.1
5.1
5
5
3.8
3.8
3.2
3.2
3.1
3.1
3
3
2.8
2.8
2.6
2.6
2.5
2.5
0
low
lat
28
13
9
7.5
6
5.5
5
4.5
4.4
4.1
3.8
3.2
3.1
3
2.8
2.6
2.5
0
depth
in
meters
0
125
250
375
500
625
750
875
1000
1125
1250
1375
1500
1625
1750
1875
2000
1750
1875
2000
ANALYSIS OF DATA
1. Describe the general shape of the temperature depth curve:
a) at low latitudes
c) at mid latitudes in winter
b) at mid latitudes in summer
d) at high latitudes
2. (a) Label and (use arrows) the three temperature layers for each location: Surface Layer, Thermocline, Deep and
Bottom Layer. (b) Name the locations for which this task is difficult or nearly impossible.
3. Which two locations indicated by your graphs might require the use of a wetsuit (or drysuit) to prevent hypothermia when swimming in the ocean? Why?
4. Approximately where (at what depth) is the primary thermocline:
a) at low latitudes
c) at mid latitudes in winter
b) at mid latitudes in summer
d) at high latitudes
5. Calculate the rate at which the overall temperature drops in OC for each 100 meters, within the first 125 meters of
the water column:
a) at low latitudes
c) at mid latitudes in winter
b) at mid latitudes in summer
d) at high latitudes
[Hint: subtract the temperature at 125m from the surface temperature, then divide by 125. Multiply your answer by
100].
6. Which regions show: (a) the most rapid temperature decline, and (b) the slowest temperature decline, within the
upper 125 meters of the ocean?
7. Calculate the rate at which the overall temperature drops in OC per 100 meters, between 750 and 1,750 meters (a
1,000 meter interval) in the water column:
a) at low latitudes
c) at mid latitudes in winter
b) at mid latitudes in summer
d) at high latitudes
[Hint: subtract the temperature at 1,750 meters from the temperature at 750 meters, then divide by 1,000. Multiply
your answer by 100].
6. Which regions (a) show the most rapid temperature decline, and (b) the slowest temperature decline, below 750
meters in the ocean?
8. Extrapolate the data as depicted on your temperature profile graphs and predict the water temperature at a depth
of 3000 m:
a) at low latitudes
c) at mid latitudes in winter
b) at mid latitudes in summer
d) at high latitudes
9. Write a short summary explaining what happens to the water temperature profile from the surface to 125 meters at
various latitudes.
10. Write a short summary explaining what happens to the water temperature profile below 750 meters at various
latitudes.
11- (Outside research) Notice that the temperature depth profile for high latitudes shows a drastic decline in temperature at an approximate depth of 125 meters, then increases in temperature down to 250 meters, beyond which
there is a continual and gradual decline. This “hook” in the profile which represents a very cold water layer sandwiched between warmer surface, and warmer deeper water, is very unusual. Knowing that water temperatures for
layers according to their density, explain the presence of this “hook” in the graph. [Hint: the “hook” is known as a
dicothermal layer].
TEMPERATURE vs DEPTH
temperature (C)
0
125
tropical
250
polar
winter
summer
375
mid latitudes
30
25
20
15
5
0
10
surface
500
625
750
875
1000
1125
depth (meters)
1250
1375
1500
1625
1750
TEACHER’S GUIDE:
TEMPERATURE vs DEPTH
temperature (C)
30
25
20
15
5
0
10
surface
0
125
tropical
250
polar
winter
summer
375
mid latitudes
500
625
750
1000
1125
depth (meters)
875
Most of the major thermoclines, if present, occur fairly shallow, just below the
surface, no matter the latitude. The deep and bottom waters of all oceans and
all latitudes are uniformly cold (there are no diurnal cycles or seasonal changes in
the deep).
The most well developed thermoclines are at low latitudes and mid latitudes
during the summer, given the transition from warm surface to uniformly cold
deep and bottom water.
Rates of temperature decline in OC / meter:
1250
1375
1500
1625
Upper 125 meters;
High Lat
0 - 7.5 / 125 = -0.0600*100=
Mid Sum
10.2 - 18 / 125 = -0.0624*100=
Mid Win
0.0 - 0.0 /125 = +/- 0.00*100=
Low Lat
13 - 28 / 125 = - 0.1440* 100=
-6.0 OC / 100 meters
-6.24 OC / 100 meters
0.00 OC / 100 meters
-1.44 OC / 100 meters
Below 750 meters:
High Lat
1.5 - 2.75 / 125 = - 0.00125*100=
Mid Sum
2.8 - 6.5 / 125 = - 0.02960 *100=
Mid Win
2.8 - 6.5 / 125 = - 0.02960*100=
Low Lat
2.8 - 5 / 125 = -0.01760*100=
-0.125 OC / 100 meters
-2.96 OC / 100 meters
-2.96 OC / 100 meters
-1.76 OC / 100 meters
1750
The dicothermal layer : A vertical ocean layer sometimes found in high northern latitudes. It is a cold (as low as -1.6 C) layer from 50 to 100 m sandwiched
between a warm surface and a warm deeper layer. The stability of this discontinuity is maintained because the warmer surface waters are of very low salinity,
and the warmer deep waters are much higher salinty, than the dicothermal layer
waters.